Surface integrity analysis in powder mixed EDM of Nimonic 263

Powder mixed Electrical Discharge machining (PMEDM) is an effective process in improving rate of material removal (MRR) and surface finish. But influence of powder mixed in the dielectric on the surface quality of the machined profile is an essential aspect of machining effectiveness. Nimonic 263 though imbibed with many advanced properties, is regarded as a difficult to machine materials by conventional methods. Spark erosion machining process is independent of the workpiece hardness and can machine any electrically conductive material. Hence EDM can be an effective alternative for machining Nimonic 263. But machining performance may vary depending upon the working medium. In this work, performance of spark erosion process in machining of Nimonic 263 has been evaluated using three different dielectric conditions. Kerosene has been taken as the dielectric fluid. Graphite micro powder as a conductive powder and alumina micro powder as a non-conductive powder have been added to the dielectric fluids for assaying their influence on the responses. Only the dielectric condition has been varied and all other parameters viz. pulse on time, peak current, gap voltage, duty factor and spark time have been kept constant at 20 µs, 6 A, 30 V, 42% and 3 s respectively. Dielectric breakdown voltage (DBV), surface topography, surface crack density (SCD), recast-layer thickness (RLT), microhardness have been considered as the performance measures in this study. Apart from these responses, 3D surface analysis has been carried out for the machined surfaces obtained by each of the dielectric conditions. Graphite powder mixed kerosene has been found to be the most suitable dielectric condition with best surface finish.